Under the New Energy and Distributed Power System, Cheng Ming Institute of Power Demand Side Management, Southeast University, Nanjing 210096, China The basic principles, key technical content and development status of distributed power systems, and the impact of distributed power generation on the power system are reviewed. Prospects.
23 Wind Power Wind is a natural phenomenon that people are very familiar with. It is due to the fact that the sun heats the air and the hot air rises. The cool air is supplemented by the timely flow of air and it has huge energy. Therefore, wind energy, like solar energy, is an inexhaustible source of clean, renewable energy. However, wind energy is a kind of process energy that is different from fossil energy such as coal, oil, and natural gas. It cannot be stored directly. It can only be converted into other energy before it can be stored. According to different needs, wind energy can be converted into other different forms of energy, such as mechanical energy, electrical energy, thermal energy, and so on. Due to the incomparable superiority of electric energy, converting wind energy into electric energy, ie, using wind power, has become the first choice for people to use wind energy, and has been rapidly developed in recent years. At the end of 1997, the installed capacity of wind power in the world was 7,636 MW. By the end of 2001, the capacity increased to 24,000 MW in just 4 years and the capacity increased by 214X, becoming the world's fastest growing power generation method.
Wind power generation is currently the most mature technology in the development of new energy, and the most extensive commercial development prospects for power generation. The principle of wind power generation is: natural wind blows the blades, drives the rotor of the generator and sends it to the professor, doctoral tutor, department head JEEE Senior Member Electric Power Engineering Discipline Committee of the China Electric Education Association Deputy Director, Deputy Director of the Jiangsu Institute of Electrotechnics President and Secretary General. The main research directions include: micro-motor and its measurement and control system, power electronics and motor integrated system, electric vehicle drive and control, distributed power supply technology.
Electricity. The wind turbines of wind turbines adopt horizontal axes and three-blade structures. The diameter of the blade increases with the increase of the single machine capacity. The diameter of the world's largest rotating blade reaches 66m and the height of the frame reaches 80m16. Power regulation is one of the key technologies of the wind turbine. The currently operating units mainly have 2 types of power. Adjustment method: One is the constant-pitch stall control; the other is variable pitch control. Most wind generators have aligned wind direction mechanisms and automatically wind the wind turbine in the windward condition. With the development of technology, new types of wind turbine systems such as concentrated wind power wind turbines upwind and speed limit automatic control systems have emerged. 2. 2.3.1 Types of wind turbines Wind turbine generators can be divided according to whether wind turbine generator speed is constant or not. There are two modes of constant speed operation and variable speed operation; according to the structure of the generator, there are asynchronous generators, synchronous generators, permanent magnet generators, brushless double-fed generators, and switched reluctance generators. Most of the early wind generators used asynchronous generators with a speed increase device. The power frequency AC power that is simply generated by the asynchronous generator structure can be used directly or input into the power grid via a transformer. In most cases, asynchronous wind turbine generators can be used to adjust the torque by applying low-frequency excitation to the variable resistors in the fixed-speed rotary-wire type asynchronous motor, and can also run at a variable speed. Because field currents are to be obtained from the grid, asynchronous wind power cannot generally be run off the grid alone unless excitation is obtained in some way.
Synchronous wind turbines do not require a speed-increasing drive structure and the overall structure is simple. With the advancement of power electronic converter technology, advanced synchronous wind power generation often adopts AC-DC-AC access method, that is, the AC power of Xinyuan New Energy and distributed power system (below) is first converted into DC power. , and then reversed into industrial frequency AC access users or the power grid. The advantage of this type of power generation is that the generator speed does not have to be synchronized with the speed required by the grid frequency.
The permanent magnet type generator is a synchronous generator that uses a permanent magnet instead of an excitation magnetic field and has no excitation system on the structure. With the popularization of high-performance, low-cost NdFeB magnets, the permanent magnet synchronous wind generators with superior manufacturing performance and good structure have become possible.
The brushless doubly-fed motor is actually composed of two winding-type asynchronous motors and the coaxial connection of the two rotors eliminates the slip ring and the brushes. The generator can control the excitation current of the exciter under the condition that the rotation speed of the rotor changes. The frequency ensures that the frequency of the generator output current is kept constant at 50 Hz. Therefore, the brushless double-fed generator can realize variable-speed constant-frequency power generation. 2.3.2 Operation mode of wind power/4 The operation mode of wind power can be divided into independent operation, grid-connected operation and complementary operation with other power generation modes. Independent operation means that the power output by the wind turbine is stored by the battery and then used by the user. This method can be used in remote rural areas, pastoral areas, and islands where the power grid can not reach, and the general stand-alone capacity of several hundred to several dry-watts is connected to the grid. In wind-rich regions, wind turbines are installed in a certain arrangement to become wind power. All the power generated by the power station is sent to the power grid via a transformer. This is the main mode of wind power generation. The wind power is complementary to other power generation methods, such as the wind power-diesel unit complementary power generation, wind power-solar photovoltaic power generation, and wind-fuel cell power generation. This approach not only compensates for the sudden change in power generation caused by changes in wind speed, ensures balanced power supply throughout the year, but also extends battery life, while also reducing the cost of power generation for off-grid, small-user power generation systems. Get full use of it.
2.3.3 Overview of domestic and international development of wind power In the early 1970s, influenced by the oil crisis in the Middle East, wind power began to struggle. In the 1980s, construction of wind farms began in the United States and Denmark. The installed capacity of wind power in the 1990s increased at an average annual rate of 203. Europe is the most developed area of ​​wind power generation in the world. Europe's wind power generation capacity increased by 4500 MW last year, making the total power of wind power in Europe reach 17 000 MW, accounting for more than 703 wind power generation capacity in the world. As the scale of production of wind power equipment expands and the technological level increases, the cost of wind power generation is continuously decreasing. For example, the cost of wind power in the United States has decreased over the past 20 years. 803. When the first batch of wind turbines were installed in the 1980s, each dry roof was The cost of wind power is 30 cents and now only 4 cents. At the same time people are studying various new wind power technologies. It is reported that three British institutions and the University of Stuttgart, Germany, have recently begun experimenting with wind power technology between high-rise buildings. The principle of this technology is not complicated. People standing in a building will feel a windy attraction. The wall between the two floors is vertical, and the wind will not be blown away here and blown directly into the turbine, which is more concentrated than the wind in the open air. According to the calculation, this method can generate 253 more electrical energy than common wind generators. If the research is successful, it will hopefully change the city's power supply structure.
China is a country with abundant wind energy resources. The total amount of wind energy resources available for development and utilization in the country is 253 million kW. The southeast coast and its neighboring islands Xinjiang, Inner Mongolia and Gansu Hexi Corridor and other regions are rich in China’s wind resource-rich regions and have great development and utilization. value. China’s wind power generation began in the 1980s and by the end of 2000, the installed capacity of wind power in China was only 344 MW. During the “Tenth Five-Year Plan†period, China plans to add 1,192 MW of wind power. The key development points are as follows: First, the new construction of 100 MW wind farms with 3 to 5 seas Jilin Offshore Wind Farm) has achieved economies of scale; second, it encourages wind power resources but has not yet established a wind farm or non-power company to develop wind power projects.
In order to encourage the development of wind power, the State Council recently approved a preferential policy for wind power generation to impose a halving of the VAT payable. According to this new policy, China's wind power tariff will be reduced by an average of 0.05~0.06 yuan/Wh), and the new wind farm electricity price level is expected to drop below 0.5 yuan/fcWh). The introduction of this policy will have a positive impact on the industrialization of wind power generation in China.
2.4 High-Speed ​​Flywheel Energy Storage System High-speed flywheel technology was a hot spot for technological development in the 1970s and early 1980s. After the oil crisis in the Middle East, people's interest in it slowly diminished. In recent years, with the development of high-strength composite materials and low-consumption bearings, as well as the needs of distributed power supply and electric vehicle applications, high-speed flywheels have once again become a research hotspot.
High-speed flywheel energy storage system is a typical high-tech electromechanical integration system. It combines the latest magnetic levitation technology, high-speed motor technology, power electronics technology and new material technology, and it can withstand high-speed flywheels that can withstand ultra-high speed operation. The basic structure of an 18-gauge high-speed flywheel such as a magnetic suspension with a small loss of a motor and a power converter capable of highly efficient bi-directional conversion of electric energy and mechanical energy is shown.
Different from traditional mass flywheels, ultra-high-speed flywheels are light-weight and extremely fast because of wheel speeds. From the above equation, the stored energy is proportional to the moment of inertia, and the new science and technology court is proportional to the square of the speed of the flywheel. Therefore, in order to increase the energy, the flywheel speed should be increased as much as possible with the flywheel strength allowed. At present, the maximum speed of a typical high-speed flywheel is recorded at 600,000 r/min at the most advanced high speed of 30 000 to 50000 r/min. The conversion between electric energy and mechanical energy in a flywheel energy storage system is based on the motor and its control system. In reality, the rotational speed of the motor and the flywheel during the storage and release of energy from the flywheel constantly changes. Therefore, in addition to the highly efficient motor, a high-efficiency power electronic power conversion device must be provided to ensure the flywheel energy storage system. During the energy storage, the speed of the motor can be controlled to increase continuously, and when the energy is released, the frequency and voltage requirements of the load can be satisfied. The motor-generator in the flywheel energy storage system has been integrated into a single component. When it is charged, it acts as a motor, absorbing energy from the outside to accelerate the flywheel; and when discharging, it acts as a generator, converting kinetic energy into electrical energy and outputting it. At this time, the speed of the flywheel is continuously declining.For high-speed flywheel energy storage systems, there are a variety of motors to choose from: induction motors, switched reluctance motors, permanent magnet brushless DC motors, and double salient permanent magnet motors. It is worth mentioning that the new double-convex permanent magnet (DSPM) motor that has emerged in recent years has a potential feature i3*2" which is very suitable for flywheel energy storage. It is a schematic diagram of a DSPM motor, which not only has a conventional permanent magnet brushless DC High motor efficiency, no commutator and brush, no maintenance, etc. The most prominent advantage is that the permanent magnets are placed on the stator of the motor. The permanent magnets have no permanent magnets on the rotor and no windings. High-speed operation, and almost no loss of heat on the rotor, which is very important for the flywheel rotor to reduce vacuum friction loss. Because the heat generated by rotor losses under vacuum conditions is difficult to dissipate.
One of the characteristics of flywheel energy storage is that the flywheel continues to rotate at high speeds for quite a long standby time. Therefore, to maintain the rotating function of the flywheel and eliminate the friction loss of the bearing 0, this is also the key to achieving efficient flywheel by extending the bearing life. Traditional mechanical bearings have large friction coefficients and are not suitable for flywheel rotor bearing in high-speed, heavy-duty flywheel energy storage devices. However, their structure is simple, compact, and robust, and is generally used as an emergency backup bearing. In recent years, magnetic suspension bearings have outstanding advantages such as high rotation speed, no mechanical contact, no friction, no lubrication, long life, and adjustable dynamic characteristics, and are particularly suitable for application in flywheel energy storage systems because magnetic bearings are contactless. With this type of bearing, the friction loss of the flywheel can be greatly reduced. Recently, superconducting technology has also been introduced into this type of bearing. The friction loss is expected to further reduce the application prospect of the 22-wheel flywheel energy storage technology. First of all, it can be used for power grid peaking. When the grid load is at a low point, the flywheel system's motor drives the flywheel to accelerate the conversion of the electrical energy into kinetic energy. At the peak of power usage, the flywheel drives the generator to convert the kinetic energy into electrical energy.
Compared with pumped storage, flywheel energy storage systems are significantly superior to pumped storage power stations, especially in the areas where water resources are lacking, and flywheel energy storage peaking power supply should be the preferred solution. After the flywheel energy storage system is put into operation in the power grid, it can effectively adjust the load level of the power system, and at the same time, it can greatly improve the static stability and transient stability of the power system.
The flywheel energy storage unit can also be used as an adjustable reactive power supply and accident backup power supply to effectively improve the system's voltage level and power supply reliability. B. Secondly, the flywheel energy storage system can be effectively overcome by combining with new energy power generation systems such as wind energy and solar energy. The shortcomings of large changes in wind energy and solar energy over the seasons and time, and the advantages of rapid response of the flywheel system make full use of the smooth energy generation of the new energy power generation system.
In addition, the flywheel energy storage system can be installed in the electric vehicle as a power source, which is called a flywheel battery. The flywheel system can also be applied to trains, ships, and other transportation vehicles. When braking, the braking energy is converted into mechanical energy of the flywheel to be stored as a renewable energy source. When high-power work is required, the kinetic energy is released to allow the system to use 2 braking energy for reuse, thereby improving transportation. The efficiency of the tool. In addition, the flywheel system has important application value in aerospace, military equipment, medical equipment, computer stations and other places.
3 Conclusion In summary, the distributed power system closely related to new energy is a typical high-tech system, involving today's new materials technology, power electronics technology, motor drive technology, semiconductor technology, electrochemical technology, demand side management, etc. . It has a series of advantages such as small scale, short construction period, small footprint, easy operation and maintenance, high efficiency, economy, reliability, and less pollution. It can be used not only for industrial and commercial enterprises, residential communities, high-rise buildings and other users, but also for users in isolated and remote areas. Electricity, and can be incorporated into the DSM (demand-side management) system of existing power systems, providing power companies with emergency power support and other services. The mutual supplementation and coordination between distributed power supply and large-scale power supply are ideal ways to make comprehensive use of existing resources and equipment and provide users with reliable and high-quality electrical energy. Therefore, the distributed power supply will occupy an increasing proportion in the power market, especially the new load, and thus have a huge and far-reaching impact on the entire power system. The first part of the new load will be satisfied by distributed power sources. The demand for centralized power plants and long-distance transmission lines will be reduced. And, due to the role of distributed power sources in peak load filling and balanced loads, existing transmission and distribution facilities The utilization rate will be greatly increased. The transmission and distribution facilities with extremely low utilization rates and only meet the needs of the peak load science and technology facilities will no longer be necessary for construction. Secondly, the introduction of distributed power will completely change the planning and operation of traditional distribution networks. Again, the popularity of distributed power sources will have a profound impact on the direction and final pattern of the electricity market. Since users can purchase electricity from power companies, they can also use their own distributed power sources to sell power to power companies, or provide power companies with services such as peak shaving, and new relationships will be formed between power companies and users. In other industries, postal natural gas companies have entered the electricity market and opened the door to convenience. The competition in the entire power market will become more intense. Therefore, the development of new energy and distributed power systems is both an opportunity and a challenge for both the technical personnel engaged in research and development of new energy and distributed power systems and for traditional power companies. mouth
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